1. Field of the Invention
This invention pertains to a preamplifier and more specifically to a preamplifier for use with a hydrophone.
2. Description of Related Art
Hydrophone preamplifiers currently in use were designed utilizing technology that is twenty years old and even though they have undergone various modifications to the technology, the components utilized are not state-of-the-art. Within the art there exists a requirement for a hydrophone utilizing state-of-the-art electronic circuits and components.
Since the early 1960's, with the advent of thin- and thick-film integrated circuits, changes have been phenomenal in all areas of electronics. Microelectronics ushered in a new era of electronic design philosophy; multitudes of components, functions, and capabilities could be realized using three to five orders of magnitude in less physical space than prior circuitry. Integrated-logic circuits became the building blocks for digital systems, and the integrated operational amplifier (op-amps) became the building block for analog functions.
In the 1960'users of hydrophones began to phase out the tube-type preamplifiers and began to use solid-state devices. This came as a result of the proven reliability and effectiveness of the field-effect-transistor (FET) in high-impedance-input preamplifiers. By the late 1960's discrete-component solid-state designs had become the norm for standard hydrophone preamplifiers.
By the 1970's integrated circuit (IC) technology had advanced to the point that a variety of analog devices could be used in hydrophone preamplifiers. Many devices were used, but their roles have been relegated to such functions as second and succeeding amplifier stages, voltage regulators, and line drivers. In general, IC op-amps fail to perform satisfactorily with reactive inputs and have very high self-noise compared to a discrete-FET input circuit. The latter disadvantage appears to be an innate failure of all IC op-amps. To meet requirements for hydrophones that were more sensitive to sea changes, the increase in amplification brought with it an increase in noise level.
The space-saving advantages of IC's for low-noise hydrophone applications can be realized by the use of a custom-manufactured hybrid microelectronics. Performance of the hybrid, including self-noise, can be equal to or superior to its discrete-component counterpart.